Regarding
<http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.
html#weeks>:
A week begins on Sunday, not on Monday.
However, under the present assumption:
Better:
A week-year has 53 weeks if the first day of the year (January 1st)
in the proleptic Gregorian calendar is Thursday or the year is leap and the
first day of the year (January 1st) in the proleptic Gregorian calendar is
Wednesday. All other week-years have 52 weeks.
Better still:
A week-year has 53 weeks if February the 28th in the proleptic
Gregorian calendar is Saturday or February the 29th in the proleptic
Gregorian calendar is Saturday. All other week-years have 52 weeks.
Also note, x-x-big5 cannot be registered with IANA because it is already
registered for private use.
HTH,
Chris